Ceiling and wall-mounted loudspeakers are often utilized in home entertainment systems. As most listening rooms present a more or less reflective environment due to walls, furniture, and other reflective surfaces, the sound that reaches a listener's ear consists not only of direct sound, but also consists of delayed sound that has been reflected off one or more boundaries. These reflected sound waves, when added to the direct sound of the loudspeaker, cause cancellation and/or addition of the sound waves at certain frequencies, which changes the character of the sound received by the listener. A significant factor in the resulting sound from a loudspeaker system is the amount of absorption and diffusion of the sound waves present in the environment. Optimally, a room containing an entertainment system should have a balance of diffusion and absorption of sound. Most entertainment systems will sound best when the loudspeakers are set up more or less symmetrically with respect to the listener and also to room boundaries. As early reflections have the most effect on the color of the sound (due to the Haas Effect), placing loudspeakers too close to either the rear or side walls is generally not preferred.
To avoid the reflective boundary concerns, loudspeakers are typically mounted within a ceiling or wall. For aesthetic purposes, these loudspeakers are generally mounted in locations that do not provide optimal acoustics. It has been long recognized that different loudspeaker placements require different technical performance from the loudspeakers. Currently available high quality loudspeakers have deficiencies when mounted on a different plane than the listener. For example, ceiling mounted loudspeakers commonly produce sound that appears to emanate from the ceiling. Direct sound radiation from the speakers and early reflections from nearby objects combine at the listener to reinforce the effect of the sound source being in the ceiling. This directional information, or “localization”, is primarily determined by the ears from the high frequency (4 kHz-10 kHz range) content of the signal.
The human ear primarily uses three localization clues to determine the apparent position of a sound source—the interaural intensity difference (IID), the interaural time difference (ITD), and the spectral profile. The IID and ITD provide primary cues to horizontal position, but no cues to determine elevation. Because human ears are mounted in a manner that defines a horizontal plane, the IID and ITD are substantially unchanged for sound sources from a constant horizontal direction regardless of the elevation above the listening plane. The spectral profile is the dominant aural clue to the vertical localization of a sound source. In particular, the spectral profile in the 4 kHz-10 kHz range is the primary clue for elevation localization as disclosed by Tan, Jun, Liew and Gan in “Elevated Speakers Image Correction Using 3D Audio Processing”, presented at the 109th AES Convention Sep. 22-25, 2000, the text of which is fully incorporated by reference herein.
Prior inventions have sought to improve the spatial imaging of elevated speakers through the use of complex three dimensional (3D) audio signal processing and electronic filtering. While this technique has some benefit, complex signal processing and electronic filtering is undesirable due to the additional circuitry required and associated additional costs. Prior inventions have also utilized scattering features to randomize the internal sound waves of a speaker, both to prevent the formation of standing waves and to diffuse the sound field in listening rooms. However, the use of these features has not been combined with controlled reflective surfaces applied to external speaker baffles to alter the spatial imaging of the speakers. Additionally, prior inventions have used directed speakers to produce a sound field oblique to an adjacent surface in order to reduce the projection of such speakers out past the surface into the living space. However, in these prior inventions, no attention has been paid to improving the spectral profile in order to alter the spatial imaging of the sound field produced by such speakers. Rather, these speakers have the spectral profile of the location where they are mounted, regardless of wall or ceiling mounting. Some of these inventions are discussed below.
U.S. Pat. No. 2,993,557 to Miller and McDonald discloses a stereo speaker system incorporating a sound reflecting surface having the shape of a curve that is symmetrical about the centerline between said loudspeakers in order to produce an omni-directional stereophonic effect. This patent does not involve a self contained, single channel loudspeaker to be used as one channel of a multi-channel system. Further, this patent does not address spatial imaging, specifically vertical spatial imaging, and is particularly only concerned with stereophonic effects in the listening plane.
U.S. Pat. No. 3,236,949 to Atal and Schroeder discloses the use of electronic signal processing using time delays, periodic repetitions of the signals, and electronic filters, so that “ordinary stereophonic signals may be given a wider stage width”. While this patent is specifically concerned with giving ordinary stereophonic signals a wider stage width in the listening plane, it does not disclose means to reconstruct and launch the sound field from a speaker out of the listening plane towards the listener with a spectral profile that is substantially indistinguishable from that of a speaker mounted in the optimum position in the listener's plane.
U.S. Pat. No. 4,836,329 to Klayman discloses the use of a combination concave and convex semi-conical reflector to disperse the sound field of a vertically oriented loudspeaker over a wide horizontal area. While Klayman's device reflects most of the sound field with reflector surfaces that block direct sound radiation from the transducer, it does not disclose the use of an obliquely mounted electro-acoustic transducer to launch a sound field in a specific direction towards a listener with most of the direct sound radiation from the speakers going to the listener without reflection. Further, Klayman does not use controlled diffraction and reflection to modify the spectral response over the 4 kHz to 10 kHz frequency range, and hence improve spatial imaging, but rather discloses a wide-field dispersal of sound without regard to spatial imaging.
U.S. Pat. No. 5,333,202 to Okaya discloses the use of a sympathetically vibratable membrane to acoustically combine the sound field from two or more transducers. Okaya states that the device provides the acoustic equivalent of an optical hologram, providing a resultant sound field that “accurately preserves the relative position of each sound source in the aural image”. However, Okaya's device deals entirely with right-left (lateral) localization, and does not involve the effects of spectral profile on the aural localization normal to the listening plane.
U.S. Pat. No. 5,764,782 to Hayes discloses a diffuse acoustic reflector characterized by a plurality of wells, where the depth of each well is governed by a quadratic residue sequence. The Hayes device provides a resultant sound field with constant directivity over frequency, which corrects for variations of directivity with frequency in the source transducer. For the Hayes device, it is particularly important that no stray paths exist for sound radiation directly from the speaker driver into the listening environment, but that only the reflected resultant sound field enter the listening environment. Hayes however, does not provide a loudspeaker with structure that allows the oblique sound field to be diffracted to create an acoustic shadow that precludes ceiling reflections and allows more of the direct radiation from the loudspeaker to reach the listener. Further, Hayes does not provide acoustic correction of the spectral profile to improve spatial imaging.
U.S. Pat. No. 5,784,468 to Klayman uses signal processing to derive sum and difference components from a stereo signal. Klayman also discloses sending the original signal, the sum, and the difference, to groups of transducers arranged in cabinets where the various signals recombine acoustically. Klayman's device serves to provide a wider lateral soundstage using only a two channel stereo source. Klayman's device does not include transducers that produce a sound field oblique to an adjacent surface, nor does it disclose modification of the spectral profile to provide localization cues.
U.S. Pat. No. 5,832,099 to Weiner discloses the use of a speaker having an undulating rigid speaker enclosure. Weiner specifically states that “the undulating wall of the speaker system randomizes the internal sound waves, thereby preventing the formation of standing waves.” Also, Weiner discloses that “only the interior wall surface need undulate to cancel the standing waves and distortion, and that the exterior wall surface can be smooth.” Weiner does not disclose a speaker containing an acoustic feature that is specifically placed on the external surface of the front baffle to alter the spatial imaging of the radiated dynamic sound field. Additionally, Weiner does not disclose an acoustic surface treatment molded into or applied to the front baffle which is substantially flat prior to application of the acoustic surface treatment.
U.S. Pat. No. 5,870,484 to Greenberger discloses the use of a combination of a centrally located loudspeaker array with signal processing to generate a signal dependent acoustic radiation pattern. Greenberger specifically manipulates the magnitude and phase of the frequency response from 150 Hz-1500 Hz, the range where the Interaural Time Differences (ITD) dominate, in order to control and expand the lateral localization of the signal source. However, Greenberger does not discuss the spectral profile as the dominant aural cue to the vertical localization of a sound source. Greenberger also does not disclose a spectral profile in the 4 kHz-10 kHz range and does not disclose manipulation of the aural cues for elevation localization.
U.S. Pat. No. 6,031,920 to Wiener discloses the use of parabolic-curved reflective and baffle structures to focus a sound field from vertical axis coaxial speakers. In this patent, the majority of the sound radiation is reflected by the parabolic baffles. Weiner does not disclose speakers with a radiated sound field having an axis which is oblique to the vertical. Further, Wiener does not utilize controlled reflection, diffraction, and absorption in a novel arrangement to improve the spectral profile, and thus improve spatial imaging.
U.S. Pat. No. 6,069,962 to Miller uses electronics and orthogonally mounted speakers to produce stereo from a single “point source”. Miller relies on electronics to produce this result, rather than relying on acoustic design. Further, Miller does not disclose speakers that are mounted to launch a single channel sound field towards the listener such that although the speaker is mounted out of the listening plane, the listener perceives the sound source to be in the listening plane.
U.S. Pat. No. 6,134,332 to Wiener is similar to U.S. Pat. No. 6,031,920, but also discloses the use of cone and curved reflective and baffle structures to focus a sound field from oblique axis speakers. Weiner discloses placing the concave reflectors to intercept all of the direct radiation from the drivers so that all of the loudspeaker radiation is “reflected by the sound lens into a downward substantially focused beam”. Weiner does not disclose however, the use of a substantially oblique axis direct sound field with the spectral profile modified by a complex curved baffle to manipulate the aural elevation cues to move the perceived sound field to the listening plane. Further, Weiner does not disclose the use of controlled reflection, diffraction, and absorption in a novel arrangement to improve the spectral profile, and thus improve spatial imaging.
U.S. Pat. No. 6,257,365 to Hulsebus discloses the use of cone-shaped reflective and baffle structures to redirect a 360 degree horizontal sound field from vertical axis speakers. Hulsebus does not provide for direct oblique axis sound radiation from the loudspeaker and does not disclose corrections to the spectral profile to improve spatial imaging.
U.S. Pat. No. 6,516,072 to Vinogradov discloses using a series of inverted and non-inverted cone reflective and baffle structures to redirect a horizontal sound field from vertical axis midrange speakers. As with U.S. Pat. No. 6,257,365 to Hulsebus, the primary objective is to produce a horizontal sound field from vertical axis (normal to the listening plane) drivers. Vinogradov does not provide for direct oblique axis sound radiation from the loudspeaker. Vinogradov further does not disclose corrections to the spectral profile to improve spatial imaging. Rather, Vinogradov discloses that the speakers are mounted with the aperture for the reflected sound field is in or close to the listening plane. However, Vinogradov does not disclose that the speakers can be mounted outside the listening plane while projecting a perceived sound field that appears to be in the listening plane.
U.S. Pat. No. 6,766,027 to Ryan discloses an elliptical ceiling speaker with opposing angled and moveable drivers. While Ryan discloses that there are benefits to pointing the speakers in the direction of the listening area with the speaker axis oblique to the mounting surface, there is no attempt to modify to the spectral profile to improve spatial imaging. The emphasis of the Ryan patent is to allow one or more of the transducers to move and be “aimed” at the listener, while the current invention involves that the geometry defined by the transducers and the specifically curved baffle be fixed in order to modify to the spectral profile to improve spatial imaging. The Ryan patent uses no rear enclosure to control the bass frequencies, whereas the rear enclosure is part of the current invention. Further, the Ryan patent discloses to point one of the drivers away from the listening area. In the current invention, the tweeter and mid-bass drivers are pointed directly at the listening area and the only drivers that are not aimed towards the listening area the passive radiators which produce very low frequencies that are substantially non-directional.
U.S. Pat. No. 6,772,859 to D'Antonio uses a series of “tiles” arranged to produce aperiodic acoustic diffusive surfaces. D'Antonio does not disclose a plurality of grooves on the baffle is arranged so that the oblique sound field will be diffracted creating an acoustic shadow that precludes ceiling reflections and allowing more of the direct radiation from the loudspeaker to reach the listener. D'Antonio also does not disclose acoustic correction of the spectral profile.
U.S. Pat. No. 6,830,275 and U.S. Pat. No. 6,926,116 to Shea disclose an angled enclosure in the ceiling/roof of a RV so that the occupants may enjoy a sound system without hitting their heads on the speakers. While these patents disclose mounting the drivers with the axis oblique to the mounting surface and pointing towards the listening area, Shea does not disclose specially curved reflecting, absorbing and diffusing surfaces to modify the spectral profile and improve spatial imaging. Shea is primarily concerned with physically mounting the devices in the limited space provided by an RV and allows a substantial part of the transducers to lie outside of the mounting plane. Shea further does not disclose placing all of the transducers behind/above the mounting plane.
U.S. Pat. No. 6,738,483 to Betts discloses the use of a device used in conjunction with and mounted in front of a driver “in a way which effects the critical acoustical loading and atmospheric coupling thereof, while controlling and shaping the ultimate acoustic waveform so that a hemispherical polar coverage pattern results.” Betts also discloses that the unique aspect of the invention is “to distribute the acoustical energy of the driver assembly so as to provide an acoustical energy field of a true hemispherical pattern.” A hemispherical pattern only serves to reinforce the listener's localization of the speaker in the ceiling. Thus, Betts does not disclose a device that launches the acoustic energy towards the listener in such a way that the resulting sound field is substantially indistinguishable from that of a speaker mounted in the listening plane.
U.S. Pat. No. 6,996,243 to Welker uses an inverted cone reflector above a vertical axis driver to produce a 360 degree sound field to increase the ratio of reflected to direct sound in the sound field and increase the size of the apparent sound field in the listening plane. This patent discloses the use of vertical axis drivers, rather than transducers mounted with the axis that are oblique to the mounting surface and pointed towards the listening area. Welker discloses the use of a large cone shaped reflector mounted in front of the transducer such that the reflector intercepts a substantial portion of the direct sound and reflects it in a substantially horizontal direction so to distribute the sound field a full 360 degrees about the transducer's vertical axis. Welker is not designed such that the spectral profile is modified to improve spatial imaging. Further, Welker is applicable to speakers mounted in the listening plane, rather than loudspeakers that can be mounted outside of the listening plane.
U.S. Pat. No. 7,054,451 to Janse discloses the use of electronics to suppress feedback and to “beam” the sound from several speakers in a particular direction in PA applications. While the device of the Janse patent serves to “beam” the sound field, reduce echoes, and filter the audio signal with electronic processing, Janse does not use a novel acoustic pattern to modify the spectral profile and thereby launch the acoustic energy towards the listener in such a way that the resulting sound field is substantially indistinguishable from that of a speaker mounted in the listening plane.
U.S. Pat. No. 7,092,541 to Eberbach discloses the use of speakers with cardioid patterns placed only forward of the listener to create “surround sound”. This patent discloses the expansion of the apparent sound field in the listening plane. However, this patent does not discuss the use of controlled reflection, diffraction, and absorption to improve the spectral profile and thus improve the spatial imaging to launch the acoustic energy from a loudspeaker mounted outside the listening plane towards the listener in such a way that the resulting sound field is substantially indistinguishable from that of a speaker mounted in the listening plane.
Therefore, it would be advantageous to provide a self contained, single channel loudspeaker to be preferably used as one channel of a multi-channel loudspeaker system, that improves spatial imaging without the use of electronic signal processing, that applies to content in the 4 kHz to 10 kHz range, that uses an obliquely mounted electro-acoustic transducer to launch a sound field in a specific direction towards a listener with most of the direct sound radiation from the speakers traveling to the listener without reflection, that only uses controlled diffraction and reflection to modify the spectral response over the 4 kHz to 10 kHz frequency range, that causes the oblique sound field to be diffracted to create an acoustic shadow that precludes ceiling reflections and allows more of the direct radiation from the loudspeaker to reach the listener, and that reconstructs and launches the sound field that provides an aural image to the listener that is substantially indistinguishable from that of a speaker mounted in the optimum position in the listener's plane.